bpo-34044: subprocess.Popen copies startupinfo (GH-8090)

subprocess.Popen now copies the startupinfo argument to leave it unchanged: it will modify the copy, so that the same STARTUPINFO object can be used multiple times. Add subprocess.STARTUPINFO.copy() method.

Author: vstinner

Lib/subprocess.py

@@ -135,6 +135,19 @@ def __init__(self, *, dwFlags=0, hStdInput=None, hStdOutput=None,
  self.hStdError = hStdError
  self.wShowWindow = wShowWindow
  self.lpAttributeList = lpAttributeList or {"handle_list": []}
+
+ def copy(self):
+ attr_list = self.lpAttributeList.copy()
+ if 'handle_list' in attr_list:
+ attr_list['handle_list'] = list(attr_list['handle_list'])
+
+ return STARTUPINFO(dwFlags=self.dwFlags,
+ hStdInput=self.hStdInput,
+ hStdOutput=self.hStdOutput,
+ hStdError=self.hStdError,
+ wShowWindow=self.wShowWindow,
+ lpAttributeList=attr_list)
+
 else:
  import _posixsubprocess
  import select
@@ -1102,6 +1115,10 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
  # Process startup details
  if startupinfo is None:
  startupinfo = STARTUPINFO()
+ else:
+ # bpo-34044: Copy STARTUPINFO since it is modified above,
+ # so the caller can reuse it multiple times.
+ startupinfo = startupinfo.copy()
 
  use_std_handles = -1 not in (p2cread, c2pwrite, errwrite)
  if use_std_handles:

Lib/test/test_subprocess.py

@@ -2822,6 +2822,33 @@ def test_startupinfo_keywords(self):
  subprocess.call([sys.executable, "-c", "import sys; sys.exit(0)"],
  startupinfo=startupinfo)
 
+ def test_startupinfo_copy(self):
+ # bpo-34044: Popen must not modify input STARTUPINFO structure
+ startupinfo = subprocess.STARTUPINFO()
+ startupinfo.dwFlags = subprocess.STARTF_USESHOWWINDOW
+ startupinfo.wShowWindow = subprocess.SW_HIDE
+
+ # Call Popen() twice with the same startupinfo object to make sure
+ # that it's not modified
+ for _ in range(2):
+ cmd = [sys.executable, "-c", "pass"]
+ with open(os.devnull, 'w') as null:
+ proc = subprocess.Popen(cmd,
+ stdout=null,
+ stderr=subprocess.STDOUT,
+ startupinfo=startupinfo)
+ with proc:
+ proc.communicate()
+ self.assertEqual(proc.returncode, 0)
+
+ self.assertEqual(startupinfo.dwFlags,
+ subprocess.STARTF_USESHOWWINDOW)
+ self.assertIsNone(startupinfo.hStdInput)
+ self.assertIsNone(startupinfo.hStdOutput)
+ self.assertIsNone(startupinfo.hStdError)
+ self.assertEqual(startupinfo.wShowWindow, subprocess.SW_HIDE)
+ self.assertEqual(startupinfo.lpAttributeList, {"handle_list": []})
+
  def test_creationflags(self):
  # creationflags argument
  CREATE_NEW_CONSOLE = 16

Misc/NEWS.d/next/Library/2018-07-04-17-14-26.bpo-34044.KWAu4y.rst

@@ -0,0 +1,3 @@
+``subprocess.Popen`` now copies the *startupinfo* argument to leave it
+unchanged: it will modify the copy, so that the same ``STARTUPINFO`` object can
+be used multiple times.